var count = require('./calculator.js').count;
var add = require('./calculator.js').add;

console.log(count); // 0 (这里的count是对calculator.js中count的值拷贝)

add(2, 3)

console.log(count); // 0 (calculator.js中变量值的改变不会对这里拷贝的值造成影响)

count += 1

console.log(count); // 1(拷贝的值可以更改)

